Acute Care Surgery (ACS), an emerging surgical specialty, was first proposed in 2005 to address a growing crisis in access to timely and high quality care for non-trauma general surgery emergencies. This innovative care delivery model represents a re-invention of the specialty of trauma surgery. ACS was theorized by the innovators who proposed it, from their vantage point in large, academic tertiary care centers rooted in our nation's tiered, regionalized trauma system, to bring together surgeons, resources, and infrastructure to provide round-the-clock care for diseases ranging from simple and highly prevalent ones such as appendicitis and cholecystitis to less frequent but complex ones such as perforated viscus and necrotizing soft tissue infections which, like trauma, are time-sensitive conditions requiring urgent surgical evaluation and possible intervention. While single institution studies suggest widespread adoption of ACS and report a number of improvements in quality and costs of care for general surgery emergencies under ACS models, there are no agreed upon guidelines of ACS implementation. To date, there are no data showing which specific features of ACS models truly improve emergency general surgery outcomes. Therefore, Americans with general surgery emergencies still seek care at the nearest emergency room irrespective of surgeon or resource availability. The human and financial toll of delays in care, possibly inadequate care, or subsequent transfers to capable centers is currently unknown. Optimizing our national approach to patients with general surgery emergencies- much like has been done over the last 40 years for trauma patients whose care was previously also left up to the availability and willingness of a surgeon on call but is now subject to robust standardized protocols and continuous quality improvement-will both improve patient outcomes and reduce healthcare costs. Our research addresses this issue of optimizing the approach to emergency general surgery patients through robust ACS models and falls within the AHRQ's Value Portfolio. We use a multimodal approach to describe the innovation and diffusion of ACS, determine which specific structures and processes targeting emergency general surgery patients are requisite to achieve the proposed benefits of ACS, and operationalize a definition of ACS based on the measures most strongly associated with improved outcomes for patients with general surgery emergencies. Ultimately, our results will be used to create a prediction model to help emergency room physicians make point-of-care decisions on whether or not a patient with a suspected general surgery emergency needs to be transferred to an ACS capable hospital and to provide guidelines for policymakers to develop emergency general surgery assessment and triage criteria in order to most cost-effectively and equitably provide high quality care to al Americans suffering general surgery emergencies. Thus, our work is well aligned with AHRQ's mission and will address serious national public health need that is only expected to worsen based on current surgical workforce trends and the aging US population.